In communications systems, vertical and horizontal eye margins of a sampled signal are measures of system performance. The vertical eye margin at the desired sampling point should be as large as possible, such that the sampled data is the same as the original data transmitted, even with the presence of latch offset and latch sensitivity. Jitter can cause the actual sampling point to move away from the desired sampling point momentarily. The vertical eye margin at the actual sampling point is what really matters. However, the vertical eye margin at the actual sampling point varies with the sampling point. Instead, the horizontal eye margin is used. The horizontal eye margin measures the range of the sampling phases within which the vertical eye margin is above a predefined threshold. The predefined threshold defines the point beyond which the error is eliminated or minimized.
It would be desirable to implement adaptation of equalizer settings using error signals sampled at several different phases.